Hi Guys
I am in the process of buying some kit to upgrade my bike http://www.halfords.com/webapp/wcs/s...egoryId_165710

to Shimano Tiagra and have noticed there are a few different types of mech that can be bought such as small, medium and large rear mechs.

Can anybody advise what the difference is apart from size and what would be most suitable for me to buy. Planning on upgrading to a 9 speed cassette if that makes any difference.

Thanks